通过存储在 Postgresql 中带有特殊字符的变量名中来删除约束

Posted 2023-03-28

【中文标题】通过存储在 Postgresql 中带有特殊字符的变量名中来删除约束

【英文标题】：Drop constraint by stored in a variable name with special characters in Postgresql

【发布时间】：2018-10-22 06:50:22

【问题描述】：

我想删除名称未知的约束，所以我使用以下代码：

EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT '||fk_Name||';';

问题是 fk_Name 以 '~' 结尾，所以出现语法错误。

完整代码：

DO $$
DECLARE fk_Name TEXT;
BEGIN
    fk_Name := (SELECT
                tc.constraint_name
                FROM
                information_schema.table_constraints AS tc
                JOIN information_schema.key_column_usage AS kcu
                ON tc.constraint_name = kcu.constraint_name
                AND tc.table_schema = kcu.table_schema
                JOIN information_schema.constraint_column_usage AS ccu
                ON ccu.constraint_name = tc.constraint_name
                AND ccu.table_schema = tc.table_schema
                WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='IntravenousTherapyAppointment' AND ccu.table_name='MedicamentMeasurementUnit');
    IF fk_Name IS NOT NULL THEN
        EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT '||fk_Name||';';
    END IF;
END $$;

【参考方案1】：

这应该可以解决您的问题：

DO $$
DECLARE fk_Name TEXT;
BEGIN
    fk_Name := (SELECT
                tc.constraint_name
                FROM
                information_schema.table_constraints AS tc
                JOIN information_schema.key_column_usage AS kcu
                ON tc.constraint_name = kcu.constraint_name
                AND tc.table_schema = kcu.table_schema
                JOIN information_schema.constraint_column_usage AS ccu
                ON ccu.constraint_name = tc.constraint_name
                AND ccu.table_schema = tc.table_schema
                WHERE constraint_type = 'FOREIGN KEY' AND tc.table_name='IntravenousTherapyAppointment' AND ccu.table_name='MedicamentMeasurementUnit');
    IF fk_Name IS NOT NULL THEN
        EXECUTE 'ALTER TABLE public."IntravenousTherapyAppointment" DROP CONSTRAINT "'||fk_Name||'";';
    END IF;
END $$;

P.S：处理带有双引号名称的对象/约束时要小心。

【讨论】：

我在我的 posgres 数据库中遇到了这种类型的变量赋值问题。我需要它类似于 oracle ：SELECT constraint_name INTO fk_Name。 PL 脚本中的一个好主意是使用 RAISE NOTICE 'Some text to be logged out'；查看脚本导航到的位置。